Anomalous magnetisation in a Fe_3Pt-FeRh film occurring at T~120 K in the field-cooled-cooling curves for low magnetic fields

We report on an anomalous magnetization observed with temperature for low magnetic fields applied in the plane of a film formed by a thin layer of Fe-Rh deposited on a thin foil of ordered Fe${}_3$Pt. The anomalous effect resembles a metamagnetic transition and occur only in the field-cooled-cooling magnetization curve at temperatures near 120 K. We also observe an aging effect which broads the metamagnetic-like transition suggesting the existence of Fe-Rh antiferromagnetic clusters which apparently are too small to be detected by the x-ray diffraction.The X-Ray diffractogram obtained in the Fe-Rh surface of the film do not show the Fe-Rh antiferromagnetic phase (a=2.98 $\mathring{A}$) but peaks at same locations of those found for the pure ordered Fe${}_3$Pt film (a=3.72 $\mathring{A}$)